Density-mediated metabolic rate in <i>Daphnia magna</i> interacted with temperature

Zooplankton change metabolic function as a physiological response to crowding. Yet it is unclear whether zooplankton physiological responses also change according to species and measurement conditions, and whether the physiological responses to crowding are also changed by temperature. Further investigations are essential to unravel the intricate interplay between crowding-induced stress, energy allocation strategies, and behavioral adaptations. In this study, we determined the metabolic rates of cladoceran <i>Daphnia magna</i> in three different densities (1, 10, and 20 individuals per 50 ml) at two temperatures (10 and 20 °C) using a highly accurate optical oxygen meter. We aimed to clarify how crowding and temperature together affect metabolic rate. At both temperatures, metabolic rates of <i>D. magna</i> in the two crowded treatments were significantly lower than those in a single treatment, and as temperature decreased, so the rates of metabolic decrease slowed. <i>Q</i>₁₀ values varied from 1.63 for the 20 individuals per 50 ml treatment, to 2.29 for the 1 individual per 50 ml treatment. This suggests that the slowing down of metabolic rates due to crowding is slightly less pronounced at lower temperatures and may be linked to reduced food consumption.

浮游动物可通过改变代谢功能，作为应对拥挤胁迫的生理响应。然而目前尚不明确，浮游动物的生理响应是否会随物种及测量条件发生变化，同时针对拥挤胁迫的生理响应是否也会受温度调控。因此亟需开展进一步研究，以阐明拥挤诱导胁迫、能量分配策略与行为适应之间的复杂互作关系。本研究采用高精度光学溶氧仪，测定了两种温度（10℃与20℃）下，三种不同种群密度（每50mL水体分别放置1、10、20只）的枝角类生物大型溞（*Daphnia magna*）的代谢速率，旨在明确拥挤胁迫与温度如何共同作用于代谢速率。在两种温度条件下，两组拥挤处理组的大型溞代谢速率均显著低于单只个体处理组；且随着温度降低，代谢速率的下降幅度趋于减缓。温度系数Q₁₀值范围为每50mL 20只处理组的1.63，至每50mL 1只处理组的2.29。这表明，拥挤胁迫导致的代谢速率减缓现象在较低温度下略有减弱，且该现象可能与摄食量减少存在关联。